Ultraviolet and visual light can damage wood; so many finishes include chemicals for UV protection. The efficacy of these chemicals depends on a wide variety of factors, but at a fundamental level it is related to their ability to absorb or reflect strongly over a wide range of frequencies. This report describes the use of UV/Visible spectrophotometry to measure the transmittance of light radiation through finishes. The development method was applied to measuring the effects of additives and to comparing commercial finishes.